The present invention relates to an optical fiber connector system. More particularly, the present invention relates to a connector assembly for optically coupling optical devices mounted on planar substrates oriented at intersecting angles with respect to each other.
The use of optical fibers for high-volume high-speed communication and data transfer is well established. As the volume of transmitted information grows, the desire for optical fiber cables including multiple optical fibers, and of systems using cables containing multiple optical fibers, has increased.
In traditional cabinet designs, such as a telephone exchange, the cabinet comprises a box having a plurality of internal slots, generally parallel to each other. Components are mounted on planar substrates, to form cards known as circuit boards. A recent technological goal has been the incorporation of optical and opto-electronic devices coupled by optical waveguide buses on the boards. In one preferred embodiment, the optical fibers are arranged in multi-fiber parallel arrays, forming parallel communications buses. The resulting optical cards would desirably be designed to slide into the slots or racks within the cabinet and to interconnect with other components and other boards.
The use of the optical circuit boards in the racked arrangement of traditional electronic cabinets presents new connectorization challenges. Within the cabinet structure, it is common for devices to be mounted on boards that define intersecting planes, such as the perpendicular arrangement of a motherboard and a backplane. A xe2x80x9cbackplanexe2x80x9d derives its name from the back (distal) plane in a parallelepipedal cabinet and generally is orthogonal to the printed circuit (PC) board cards. The term backplane in the present invention refers to an interconnection plane where a multiplicity of interconnections may be made, such as with a common bus or other external devices. For explanation purposes, a backplane is described as having a front or interior face and a back or exterior face.
The need exists to provide a means to allow optical signals to xe2x80x9cturn the corner,xe2x80x9d that is, to couple optically components on intersecting boards. However, optical waveguide signal transmission relies on total internal reflection of a light signal within the waveguide and optical waveguides bent at sharp angles suffer unacceptable microbend and/or macrobend optical signal losses. Furthermore, many optical waveguides, such as glass optical fibers, are fragile and may fracture or crack when bent past a certain physical tolerance. Different optical waveguides have different optical transmission and physical integrity qualities. The acceptable signal losses and the physical flexibility of a waveguide determine the acceptable radius of curvature for a particular fiber. The radius of this curve is defined as the critical bend radius for the particular fiber. It is therefore desirable that an inter-card connector system account for the critical bend radius of the optical waveguide connections.
In addition, in cabinet connection applications, users slide the cards in and out of the cabinet racks. It would be desirable to have a disconnectable fiber connection along the insertion axis of each card. Such a connection would preferably be capable of absorbing excessive insertion pressure, such as that caused by a user xe2x80x9cjamming inxe2x80x9d a card, while still maintaining the desired bend radius and exerting sufficient connection pressure along the ends of the fibers to ensure a reliable optical connection.
Finally, it would be desirable for a multi-fiber inter-plane connector to maintain the parallel alignment of the fibers in the optical bus, for ease of connectorization, without subjecting the fibers to uneven twisting or tensile stresses.
For the purposes of the present description, the axis of interconnection along one of the planes is called the longitudinal or y-axis and is defined by the longitudinal alignment of the optical fibers at the point of connection. Generally, in backplane applications, the longitudinal axis is collinear with the insertion axis of the cards and the axis of connection of the optical fibers in and out of the cabinets. The lateral or x-axis is defined by the axis of connection of the optical fibers on the other substrate plane. Generally, the x and y-axes are mutually perpendicular. Finally, the intersection of the two planes defines a transverse or z-axis, also called the intersection axis. Again, in most applications, the z-axis is orthogonal to the x-axis and y-axis.
Different connection methods have been suggested to couple optical circuit cards. Some references, such as U.S. Pat. Nos. 4,498,717 or 5,639,263, suggest the use of electrical connections between the intersecting substrates. However, the use of electrical connections necessitates the conversion of optical signals to electrical signals and vice versa at each connection. Optical fiber xe2x80x9cjumperxe2x80x9d cables have been suggested, but such individual optical fibers are susceptible to damage and to the risk of bending past the critical bend radius of the fiber.
To support the fibers, some references, such as U.S. Pat. Nos. 5,155,785 and 5,204,925, discuss placing the fibers in groves or channels or laminating the fibers to a flexible substrate. In these patents, the optical backplane is a custom backplane designed to contain the optical fibers within it. The bend radius of the fiber is controlled by the thickness of the backplane. As described in the ""785 reference, xe2x80x9c[t]he optical backplane member 32 has a sufficient thickness between opposite surfaces 33 and 34 to provide an appropriately large radius of curvature through which each optical fiber must be bent in making the connection between the surface 34 and the MAC connector 25. Typical dimensions of the backplane 32 are eight inches by sixteen inches by three inches in thickness. It can be shown that, for digital transmission at practical power levels, the minimum radius of curvature through which an optical fiber may be bent without incurring significant losses is one inchxe2x80x9d.
An obvious constraint of such design is the required use of specially grooved very thick substrates. The backplane design is described as containing xe2x80x9ca complex arrangement of arcuate grooves of varying depth . . . xe2x80x9d and as such would appear to be very difficult to design and manufacture for each application.
U.S. Pat. No. 5,793,919, references a backplane interconnect system that connects optical signals from a number of daughter cards on to an optical fiber backplane bus. As such, the backplane fibers are not coupled end to end with the daughter card fibers in a point to point connection system, and the backplane fibers are not terminated in a backplane connector at each daughter card location. The optical signals from each daughter card are added to the continuous fibers of the backplane bus, and the bus fibers carry all signals simultaneously to all coupling locations. This design requires a special xe2x80x9cDxe2x80x9d fiber profile to enable this longitudinal coupling to take place.
U.S. Pat. No. 5,204,925 relates to an interconnection system containing termination tabs that connect through openings in the electrical backplane, but do not connect to the backplane. This might be considered as an example of a custom optical jumper cable and connector system, not a backplane and connector system. The jumper cable assembly does not provide strain relief or bend radius control for the optical fibers. In use, the fibers are twisted from the plane of the optical jumper circuit in order to connect to the circuit boards. In twisting the termination tabs containing the optical fibers, a torsional force is applied to the fibers in the tab, which will impart a long-term stress on the individual fibers, or may cause the fibers to shift within the assembly in order to relieve stress.
The need remains for an effective connector for optically coupling parallel multifiber optical devices in intersecting optical boards.
A connector assembly for coupling optical devices disposed on a first and a second plane, wherein the first and second planes intersect at an intersection axis z. The connector assembly comprises an optical waveguide array, a first waveguide retaining means, and a second waveguide retaining means. The first plane is defined by a first substrate, such as a circuit card, and the second plane is defined by a second substrate. In one embodiment, the first substrate comprises a motherboard and the second substrate comprises a daughter card generally perpendicular to the motherboard. In another embodiment, the first substrate comprises a backplane and the second substrate comprises a printed circuit card generally perpendicular to the backplane.
The optical waveguide array includes a plurality of waveguides, such as optical fibers arranged in a parallel array. In one exemplary embodiment, the first and second waveguide arrays are optical buses optically coupled to optical devices. The waveguides have a minimum desired bend radius, which is at least as large as the critical bend radius for the waveguides.
The first waveguide retaining means secures a first end portion of the optical waveguide array to the first plane. The second waveguide retaining means secures a second end portion of the optical waveguide array to the second plane. The first and second waveguide retaining means secure the first and second end portions of the waveguide array at minimum predetermined first and second distances from the intersection axis z. The waveguide array arches between the first and the second plane having a bend radius equal to or greater than the minimum desired bend radius.
In one exemplary embodiment, the connector assembly optically couples a first optical waveguide array attached/mounted to a first substrate to an optical device on an intersecting second substrate. The first waveguide array includes a plurality of parallel optical waveguides having a minimum desired bend radius. The first and the second substrate define a first and a second plane respectively and the longitudinal direction of the first waveguide array defines a first axis. The intersection of the two planes defines an intersection axis that is generally perpendicular to the first axis. The first waveguide array has a substrate portion mounted to the first substrate (such as by adhesive or another connector), a midspan portion, and an end portion. The connector assembly includes a first connector mounted to the first substrate and aligned along a second axis generally perpendicular to the intersection axis. The first connector has a first retaining mechanism that receives and retains the end portion of the first optical waveguide array, where the end portion is suspended over the first plane at a distance along the second axis that is at least equal to the minimum desired bend radius. The midspan portion of the second optical waveguide array describes a suspended bend curve between the first and the second plane, the suspended bend curve having a bend radius that is equal to or greater than the desired minimum bend radius.
In this exemplary embodiment, the waveguide array comprises a plurality of parallel optical fibers and the first retaining mechanism comprises a v-grooved fiber receiving surface that accommodates the parallel optical fibers of the first optical waveguide array. A cover snaps over the receiving surface and secures the parallel optical fibers against the fiber-receiving surface. The cover includes a chamfered portion at the end closer to the intersection axis, the chamfered portion describing a curve having a radius at least equal to the minimum desired bend radius of the first optical waveguide array.
The connector assembly further comprises a second connector having alignment and mating features matching and coupling to the first connector. The second connector is aligned along the second axis and the second plane, the second connector including a second retaining mechanism that receives and retains a second optical waveguide array.
In the present exemplary embodiment, the first and second connectors have limited first and second ranges of movement along the second axis. The first retaining mechanism is slidably mounted parallel to the second substrate and allows the end portion a first range of movement along the second axis, the first range of movement determining a maximum and a minimum position with respect to the first plane. The first connector includes a first connector block and a mounting assembly, the first connector block being slidably mounted onto the mounting assembly. The mounting assembly includes at least one detent member that limits the range of motion of the first connector block. The minimum and maximum positions are selected such that the radius of the suspended bend curve of the midspan portion at either position is at least equal to the minimum desired bend radius for the first optical waveguide array. The first and the second connector include biasing elements, such as springs, that bias the first and second connectors towards each other and into a desired connected position. A cover element slides over the first and the second connector. The cover element has internal geometry features that match external geometry features of the first and second connectors and that align the first and second connectors.
In a second exemplary embodiment, the connector assembly may further comprise a third connector that retains the substrate portion of the first optical waveguide array. The third connector is slidably coupled to the first substrate, such as by tabs secured in a longitudinal slot. The slidable coupling allows a third range of motion for the substrate portion of the waveguide array along the first axis. The third range of motion has a maximum and a minimum value such that the bend radius of the suspended portion is at all times at least equal to the minimum desired bend radius.
Other exemplary embodiments may include a plurality of connector pairs contained in a single shell. The connector pairs may be staggered or planarly aligned.
In other exemplary embodiments, the second connector comprises a receptacle having an optical device, wherein the receptacle optically connects to the first connector. The third connector also may connect to a receptacle having an optical device.
In yet other examplary embodiments, the optical waveguide array may be a flexible array of polymer waveguides, such as those disclosed in U.S. Pat. No. 5,265,184.